This invention relates to a static mixing device for homogenizing or blending a single stream of viscous material, e.g., a molten polymer or solution of polymer, to render composition of the material more uniform, or for combining two or more streams of viscous material, e.g., two different molten polymers or solutions of different polymers, to provide a single substantially homogeneous stream.
Static mixers, also referred to in the art as in-line mixers, constitute a well known category of mixing device which typically contain no moving parts but achieve mixing by directing a moving stream against stationary elements which twist and cut the stream or force it through channels or tubes. The multiple subdivisions and recombinations of the stream within a static mixer results in its being homogenized or blended, the extent of uniformity of the mixing being determined by a variety of factors, principally the design and arrangement of the stationary mixing elements and the number of stages in the mixer.
In the fiber-producing industry, static mixers are widely used in connection with a variety of manufacturing operations. Thus, e.g., in spinning a melt or solution spinning operation, a static mixer may be employed to homogenize one or more viscous polymers or a stream of spinning solution ("dope") or to intimately blend two or more such streams to provide a homogeneous stream which is then directed through a spinnerette to provide filaments. Illustrative of spinning assemblies featuring a static mixing device are those described in U.S. Pat. Nos. 2,815,532; 3,458,900; 3,701,619; 3,968,307; 4,134,954; 4,197,020; 4,307,054; and 4,414,276.
Fitzgerald et al., "Mixed-Stream Spinning of Bicomponent Fibers", Textile Research Journal, Vol. 37, No. 6, pp. 447-453, June 1967 describes a device for merging spinning solutions used in the manufacture of bicomponent acrylic fibers. The merging device is made up of an assembly of plates in which merger plates, possessing varying patterns of channels and orifices, alternate with spacer plates. The merging device does not result in a true mixing or blending of the two spinning solutions but, as the term "merging" indicates, combines the solutions along their interface to ultimately provide a bicomponent filament or heterofilament. The fiber-forming polymers in the two spinning solutions retain their separate identities in the spun fiber where they may be arranged in a sheath/core or side-by-side pattern. Thus, the Fitzgerald et al. merging device is not, technically speaking, a static mixer. Other devices which merge, but do not homogenize or blend, spinning solutions are described in U.S. Pat. Nos. 3,457,342 and 3,469,279.